1. Field of the Invention
The invention relates to melt-processible, highly-neutralized ethylene, C3 to C8 xcex1,xcex2 ethylenically unsaturated carboxylic acid copolymers and process for making them. It relates to such copolymers, neutralized to greater than 90%, particularly to those neutralized to nearly to or to 100%. These copolymers are made by incorporating a sufficient amount of specific organic acid (or salt) into the copolymer before neutralization to the high level.
The invention particularly relates to melt-processible, highly-neutralized (greater than 90%) polymer comprising (1) ethylene, C3 to C8 xcex1,xcex2 ethylenically unsaturated carboxylic acid copolymers that have their crystallinity disrupted by addition of a softening monomer or other means, and (2) sufficient amount of a non-volatile, non-migratory agent such as an organic acid (or salt) selected for its ability to substantially or totally suppress the ethylene crystallinity. Agents other than organic acids (or salts) may be used.
The invention also relates to thermoplastics that, when molded into spheres, have a coefficient of restitution of at least 0.785 (measured by firing a sphere of the thermoplastic at an initial velocity of 125 feet/second against a steel wall positioned 3 feet from the point where initial velocity and rebound velocity are determined and by dividing the rebound velocity by the initial velocity) and an Atti compression of no more than 100.
These copolymers are useful in making molded products such as golf ball components, thermoplastic shoe soles for cleated footwear, and resilient foams for sporting goods. They are particularly useful in the manufacture of one-, two-, and three-piece and multi-layered golf balls. The invention particularly relates to the spherical components (cores, centers, and one-piece balls) having a coefficient of restitution of at least 0.785 when measured at 125 feet/second and Atti compressions of 100 or less.
2. Description of Related Art
Typical premium golf balls include three-piece balls, two-piece balls and multi-layered balls. xe2x80x9cThree-piecexe2x80x9d balls typically have a spherical molded center, elastomeric thread-like material wound around the center, and either a thermoplastic or thermoset cover. xe2x80x9cTwo-piecexe2x80x9d balls typically have a spherical molded core covered with a thermoplastic material. xe2x80x9cMulti-layeredxe2x80x9d balls typically have a spherical molded core and one or more intermediate layers or mantles between the core and a cover.
Three-piece centers and two-piece and multi-layer-cores have traditionally been made using a thermoset rubber such as polybutadiene rubber. With thermoset rubber, complex multi-step processes are needed to make cores and centers and scrap cannot be recycled. Attempts to solve these difficulties by substituting a thermoplastic for the thermoset have had limited success. Also, attempts to make premium one-piece balls have been unsuccessful. See U.S. Pat. No. 5,155,157, UK Patent Application 2,164,342A and WO 92/12206. Balls, cores and centers made based on these references have a high cost and lack properties such as durability, softness (low Atti compression), and resilience to make them useful in premium balls.
One thermoplastic that has found utility in golf ball components and other applications for a long time are ionomers of copolymers of alpha olefins, particularly ethylene, and C3-8 xcex1,xcex2 ethylenically unsaturated carboxylic acid. U.S. Pat. No. 3,264,272 (Rees) teaches methods for making such ionomers from xe2x80x9cdirectxe2x80x9d acid copolymers. xe2x80x9cDirectxe2x80x9d copolymers are polymers polymerized by adding all monomers simultaneously, as distinct from a graft copolymer, where another monomer is grafted onto an existing polymer, often by a subsequent free radical reaction. A process for preparing the acid copolymers on which the ionomers are based is described in U.S. Pat. No. 4,351,931.
The acid copolymers may contain a third xe2x80x9csofteningxe2x80x9d monomer that disrupts the crystallinity of the polymer. These acid copolymers, when the alpha olefin is ethylene, can be described as an E/X/Y copolymers wherein E is ethylene, X is the xcex1,xcex2 ethylenically unsaturated carboxylic acid, particularly acylic and methacrylic acid, and Y is the softening co-monomer. Preferred softening co-monomers are C1 to C8 alkyl acrylate or methacrylate esters. X and Y can be present in a wide range of percentages, X typically up to about 35 weight percent (wt. %) of the polymer and Y typically up to about 50 weight percent of the polymer.
A wide range of cations is known for neutralizing acid moieties in the acid copolymer. The degree of neutralization is known to vary over a wide range. Typical cations include lithium, sodium, potassium, magnesium, calcium, barium, lead, tin, zinc, aluminum, and combinations of such cations. Neutralization to 90% and higher, including up to 100%, is known, but such a high degree of neutralization results in a loss of melt-processibility or properties such as elongation and toughness. This is particularly so for copolymers with high acid levels and when using cations other than barium, lead and tin to neutralize the copolymer.
The thermoplastic composition of this invention comprises a polymer which, when formed into a sphere that is 1.50 to 1.54 inches in diameter, has a coefficient of restitution (COR) when measured by firing the sphere at an initial velocity of 125 feet/second against a steel plate positioned 3 feet from the point where initial velocity and rebound velocity are determined and by dividing the rebound velocity from the plate by the initial velocity and an Atti compression of no more than 100.
The thermoplastic composition of this invention preferably comprises (a) aliphatic, mono-functional organic acid(s) having fewer than 36 carbon atoms; and (b) ethylene, C3 to C8 xcex1,xcex2 ethylenically unsaturated carboxylic acid copolymer(s) and ionomer(s) thereof, wherein greater than 90%, preferably near 100%, and more preferably 100% of all the acid of (a) and (b) are neutralized.
The thermopastic composition preferably comprises melt-processible, highly-neutralized (greater than 90%, preferably near 100%, and more preferably 100%) polymer of (1) ethylene, C3 to C8 xcex1,xcex2 ethylenically unsaturated carboxylic acid copolymers that have their crystallinity disrupted by addition of a softening monomer or other means such as high acid levels, and (2) non-volatile, non-migratory agents such as organic acids (or salts) selected for their ability to substantially or totally suppress any remaining ethylene crystallinity. Agents other than organic acids (or salts) may be used.
It has been found that, by modifying an acid copolymer or ionomer with a sufficient amount of specific organic acids (or salts thereof); it is possible to highly neutralize the acid copolymer without losing processibility or properties such as elongation and toughness. The organic acids employed in the present invention are aliphatic, mono-functional, saturated or unsaturated organic acids, particularly those having fewer than 36 carbon atoms, and particularly those that are non-volatile and non-migratory and exhibit ionic array plasticizing and ethylene crystallinity suppression properties.
With the addition of sufficient organic acid, greater than 90%, nearly 100%, and preferably 100% of the acid moieties in the acid copolymer from which the ionomer is made can be neutralized without losing the processibility and properties of elongation and toughness.
The melt-processible, highly-neutralized acid copolymer ionomer can be produced by
(a) melt-blending (1) ethylene xcex1,xcex2 ethylenically unsaturated C3-8 carboxylic acid copolymer(s) or melt-processible ionomer(s) thereof (ionomers that are not neutralized to the level that they have become intractable, that is not melt-processible) with (1) one or more aliphatic, mono-functional, saturated or unsaturated organic acids having fewer than 36 carbon atoms or salts of the organic acids, and then concurrently or subsequently
(b) Adding a sufficient amount of a cation source to increase the level of neutralization all the acid moieties (including those in the acid copolymer and in the organic acid) to greater than 90%, preferably near 100%, more preferably to 100%.
Preferably, highly-neutralized thermoplastics of this invention can be produced by
(a) melt-blending (1) ethylene, xcex1,xcex2 ethylenically unsaturated C3-8 carboxylic acid copolymer(s) or melt-processible ionomer(s) thereof that have their crystallinity disrupted by addition of a softening monomer or other means with (2) sufficient non-volatile, non-migratory agents to substantially remove the remaining ethylene crystallinity, and then concurrently or subsequently
(b) Adding a sufficient amount of a cation source to increase the level of neutralization all the acid moieties (including those in the acid copolymer and in the organic acid if the non-volatile, non-migratory agent is an organic acid) to greater than 90%, preferably near 100%, more preferably to 100%.